Treatment of manganese ores for the recovery of manganese as manganese carbonate



Dec. 9, 1952Y A R. s. DEAN r-:rAL 2,621,107

TREATMENT oE MANGANESE oREs EoR THE RECOVERY -oENANGANEsE As MANGANESEcAREoNATE Filed Sept. l0, 1949 INV'ENTORS UNITED STATES ENT TREATMENT FMANGANESE ORES FOR THE RECOVERY OF MANGANESE AS MAN- GANESE CARBONATEReginald S. Dean and Abraham L. Fox, Washington, D. C.; said Foxassigner to said Dean Application September l0, 1949, Serial No. 115,122

GFFICE 6 Claims.

1 This invention relates to processes for recovering manganese from itsores. It relates particularly to processes of dissolving manganous oxidein ammoniaca-l solutions to which carbon dioxide 2 In this applicationthe composition of solutions will be referred to either in terms of thematerials from which they are made, as has just been done for the testsreported in Table I,

has been added and precipitating manganous 5 or in terms of the NH3, CO2and Mn which they carbonate from them. It has for its aim the contain.When the latter procedure is followed, improvement of such processes tomake them it will be understood that these are components more rapid andmore eicient. in the physico-chemical sense, that is, the solu- Inco-pending applications each of us has distion being described could bearrived at by the closed processes for recovering manganese carreactionof the three components. No inference bonate from ores. These co-pendingapplications is intended as to the molecular species present are SerialNo. 65,721, nled December 16, 1948, in any givensolution. and Serial No.57,376, iiled October 29, 1948. The TABLE I processes described in theseapplications disclose the following steps: Time of un ex- 1. Convertingthe manganese content of the Leach' Accelerating agent `iction, minutesement ore to manganous oxide.

2. Dissolving the inanaanous oxide in an aque- 15 11.5 g.NH oiLHso eussolution made from 50-300 grams of NH3 per 3o 17.5 giiinnsoi l' 1.04m. a46.0 liter andlfrom 38.5 90.0 grams of CO2 per liter, 20 1g 025g*Fmmmsomu 80.0 by agitation at atmospheric temperature for up g (30927-80,0 to one hour, to produce a solution containing up m Fe(NHo2(SOo2.-.79.6 D2 04h- 89.0 to about 100 grains of manganese per liter as a omisaturated H2803. 515 Complex Salt mg. llowiercd iron 3. Separating thesolution from the residue mglNsIIIIIIIII 7020 of the ore.

4. Precipitating part or all of the manganese as carbonate from thesolution by dilution with Water, by removal of ammonia, by heating underpressure or a combination of these steps.

5. Separating the manganese carbonate from the solution.

6. Regenera-ting the solution for re-use in the second step byevaporation, adding CO2, adding ammonia or by a combination of these.

The rst, third and fth steps are conventional fand may be cairied out bythe usual rrethods of :chemical engineering. Steps 2, 4 and 6 aredisclosed in our cio-pending applications. It is the particular aim ofthe present invention to im'- prove these steps of the process.

We have found that certain addition agents These tests show thathydroxylainine salts, ferrous salts and soluble sulphides aresignicantly more effective than the other materials tried.

Further tests Were made on hydroxylamine acid sulphate and on sodiumsulphide to determine the effect of varying amounts of these additionsand Varying periods of agitation. The results are shown n Tables II andIII.

TABLE II Hydroccylamine acid sulphate as addition agent [Tao determineminimum amounts of NH2OH.HSO4 requiredkand effect of time, 12 leacheswere prepared each consisting of. 8 gm. of well-reduced ore, 100 m1. ofaqua ammonia, 10 gm. of ammonium carbonate and NH1QH-HSO4 as shown. Theleaches were made on a shaking machine in sealed flasks] substantiallyincrease the rate of extraction and M 'the total extraction of themanganese from the Timaminutes NHzOI-HSO zalcltn, reduced ore when addedin the leaching step. g' percent The addition agents which we have foundeffective are reducing agents and include hy- 1g droxylamine salts,ferrous salts, sulphites and 25 e115 sulphides. 5g il@ Table I shows theeiect of several reducing io @SI1 agents when used in a test leachcontaining 8 grams of Well-reduced ore, 100 inilliliters of aqua 0 48-7ammonia containing 28% NH3 and 10 grams ci gig commercial ammoniumcarbonate, shaking at 90-0 a fixed rate in the absence of air.

3 TABLE In Sodium sulphide as addition agent [Foui grams of ore weretreated with 100 nil. of aqua ammonia containing 10 gm. (NHQgCO, theleach being ifiliade im the shaking machine for 30 minutes in sealed asis.

Y Mn ex- Test No. Angus traction, g' percent 1 l0 Q8. 5 2 50 U6. 5

In view of the cost of hydroxylamine and the fact that sodium sulphidealso serves to precipitate certain impurities, further testson sulphideswere initiated. It was found that the use of sodium sulphide brought-.about the inclusion of sodium in the precipitated manganese carbonate,consequently-ammonium sulphide was used. The resultsrof tests withammonium sulphide as an accelerating agent are shown in Table IV.

.TABLE IV [In these tests enough CO2 was added to produce aconcentration of 3.7 tools/liter, and the Weight of ore used was 146g./liter in each test. The ammonium sulphide solu- Ytioncontnined 15%sulphur by Weight. The maximum manganese concentration obtained, V83grams per liter, corresponded to 85% extraction of the manganese] Itwill be seen that with 4 cc. `of ammonium sulphide as accelerator aconcentration of 'l2-75 grams per liter of manganese is obtained in theremarkably short period of 5 minutes and that this amount is notsubstantially increased by increasing either time of leaching or amountof ammonium sulphide. On the other hand increase in concentration ofammonium sulphide interferes with the settling of the residue from thesolution. At 8 cc./liter the solution settles with great difliculty anddoes not give any clear solution at all in one to two hours. At 5cc./liter we can get 85 cc. of perfectly clear solution out of 100 cc.leach slurry in five hours.

From the results of the tests described it is concluded that the use ofammonium sulphide as an accelerator has definite advantages which couldnot have been predicted from the tests with sodium sulphide, that theamount used is highly critical, and that for the ore used in the testsdescribed the amount used should be equivalent to 4.0 to 6.0 millilitersof a solution of colorless ammonium sulphide containing 15% sulphur byweight, per liter of lixiviant.

It will be understood that the amount of am.- monium sulphide requiredto produce the maximum acceleration of the solution of manganous oxideand at the same time provide rapid settling of the residue will varysomewhat with the ore. If, for example, the ore contains copper as animpurity, additional ammonium sulphide will be required to bring aboutthe optimum results. Likewise, if the ore contains a course grainedresidue so that adsorption on it is reduced to a.

minimum, the amount of ammonium sulphide will be somewhat reduced.

It has been found that with ores high in iron the reducing of the oreshould be carried out so as to bring the iron as far as possible intothe state of Fe3O4. In such ores, however, it has been found desirableto use ammonium polysulphide rather than ammonium sulphide as theaccelerator. The optimum amount and sulphur content of the ammoniumsulphide accelerator depend on the iron contentof the ore and its stateof oxidation. It must, therefore, be determined for each ore androasting condition.

In our previous disclosures of the leaching step we have carried out theprocess at atmospheric temperature. The yeffect of temperature outsidethis range might well be important as well as variations within it.Hence we have studied the effect of temperature on the rate of theleaching step. The results are shown in Table V.

TABLE V Effect of-temperature on extraction Mn cor cnt of peg a tTemperature, C.

liquor. g ,/l.

Optimum extraction of manganese requires a temperature between 10 C. to30 C. although the drop in extraction with increasing temperature is notlarge.

The concentration of ammoniain the leach solution is an important factorin the extraction of manganese. In Table VI is shown the effect ofvariable ammonia concentration on the concentration of manganese in theleach solution after 45 and 60 minutes agitation, respectively. The twolengths of time Aare given to show that with ammonia concentrations of15 to 1G mols per liter there is no precipitation of the dissolvedmanganese in the additional 15 minutes of agitation whereas at lowerconcentrations the amount of this precipitation becomes signiiicant.

TABLE VI Ammonia as a factor both in pregnant liquor build-up and instability of high-manganese solutions All ofv these tests were run underidentical conditions using an amount of ore, ammonium sulphide, andtemperature of leaching which had been found to give gOOd extractionsfor this particular ore. They are, therefore, comparable amongthemselves but not necessarily with other tests described in thisapplication. In the tests described the upper limit of ammoniaconcentration has been 16 to 17 mols per liter. This is substantiallythe maximum concentration which can be obtained at room temperature andatmospheric pressure. As shown in Table VI the amount of manganese whichis dissolved still increases a small but definite amount by increasingthe ammonia concentration from 14 mols per liter to 16 mols. A stillfurther increase may be obtained by carrying out the extraction underpressure. Under these conditions each additional mol per liter of NH3which may be dissolved will increase the grams per liter of manganese byabout 0.8 of a gram up to a maximum of about 67 grams per liter. Thisgain is in general not worth the trouble.

The eiect of carbon dioxide concentration of y the leach liquor on theamount of manganese extracted is also highly important. In our copendingapplications the upper limit of CO2 disclosed was 90 grams per liter. Wehave now found that improved results are obtained with substantiallyincreased CO2 content, preferred range being from 2.5 to 4.0 mols or atleast 110 grams CO2 per liter. Lesser concentrations are workable, butwill result in a lower concentration of manganese in the resultingpregnant liquor. This embodiment of our invention is illustrated inTable VII.

TABLE VII Eject of CO2 content of Zirz'viant on the manganese content ofpregnant liquors 6 TABLE vnr Pressure precipitation [To determine theextent of precipitation of manganese when a. pregnant liquor is heatedat varying times and emperztures, the liquor being held in heavy, sealedglass ottles.

These results were obtained with a solution ccntaining about 12 mols perliter of ammonia.

While pressure precipitation has certain advantages, it has been foundthat with ammonia. above 14 mols per liter precipitation is lesscomplete than at lower concentrations. It has, therefore, been foundnecessary to reduce the ammonia concentration to about 13 mols beforepressure precipitation. It has accordingly been found preferable toaccomplish the precipitation by heating at atmospheric pressure. Thismay be conveniently done at about 65 C. The result of heating a leachsolution containing about 52 grams per liter Mn, 3.0 mols per liter CO2and 16 mols NH3 per liter in this way is shown in Table IX.

TABLE IX Atmospheric pressure precipitation of manganese carbonate as afunction of NH3 evolution Time Mn, g./l. NH3, mols/l.

All of these tests were run in an identical manner using an amount ofreduced ore, ammonium sulphide, leaching time and temperature which werefound to give good extractions on this particular ore. The tests are,therefore. com-parable among themselves but not necessarily with othertests given in this application.

In summary then we have found that the leaching step (No. 2) in theprocess should be carried on in the presence of a critical amount ofammonium sulphide and that the ammonia and CO2 concentrations should bea minimum oi 12 mols of NH3 per liter and from 2.5 to 4.0 mols of CO2per liter. The temperature of the leaching step should be from C. to 30C. and the time not in excess of one hour. Under these conditions theratio of ore to leaching solution should be such as to provide a iinalmanganese concentration of from to S5 grams per liter at 99% extraction.

The precipitation step may be carried out as disclosed in our co-pendingapplications by dilution, by heating or by removing part of the ammoniaby evolution. We have found that if it is to be done by heating alone,this is very effectively carried on under pressure, as highertemperatures and therefore shorter times may be used. This is shown inTable VIII.

Some carbon dioxide as Well as ammonia is evolved in heating thesolution at atmospheric pressure.

We have found that in the precipitation step it is necessary to maintainthe molar ratio of CO2 to manganese in solution above a denite value orthe manganese carbonate precipitate will be less stable in air and alsoless iiltrable. This ratio has been determined to be 1.75. In thepreferred form of the present invention a considerably larger ratio willalways be present at the end of the leach period. Ordinarily the ratiowill not fall below the minimum during the precipitation step. However,we have found that the precipitation step may be accelerated bymaintaining the CO2 concentration or even increasing it duringprecipitation by adding CO2 before or during the precipitation step.This has a number of advantages. It obviates the necessity of adding CO2to regenerate the solution after separation of the manganese carbonate,the passage of CO2 into the hot solution hastens the removal of ammoniaand any CO2 passing through the solution may conveniently be absorbed inabsorption towers provided for the ammonia, thus preventing loss, andfinally since CO2 is most readily available in hot combustion gases,these may be used to heat the solution, drive on. the ammonia and, atthe same time, supply CO2 so that both precipitation and regenerationare effected in the one step.

From a consideration of Table IX it will be seen that 96.5% o'fthe'manganese is precipitated at 171.9 inolsperliterI of ammonia, sothat the arnmonia concentration of the solution is reduced by only about25% There is also, of course, some reduction in the volume of thesolution. An actual ammonia balance has shown that approximately 40% ofthe ammonia originally present in the leach solution is evolved duringthe precipitation step.

In another embodiment of our invention the solution is treated withcarbon dioxide before heating for the removal of ammonia. This may beconveniently accomplished by using combustion gases containing CO2 toheat the solution for the precipitation step and then using the thuscooled CO2 containing gas to carbonate the'next batch of solution. y

In summary, then, vthe precipitation step (No. f1)v of ourinventi'on-ispreferably carried out vby heating the solution at atmospheric pressurewhereby the ammonia concentration of the solution is reduced by about'25%, usually' from about 16 mols per liter to 12 mols per liter, the'carbon dioxide'content'ofthe solution being maintained above 1.75 molsper liter. In this way the manganese content of the solution may bereduced to less than 7.() grams per liter. The regeneration of thesolution stepKNo. 6) vis preferably carriedout in two parts, theaddition of CO2 to make up for that to be taken outof 'the solutionas'manganese carbonate being madeahead of the precipitation step orconcurrently'with it. This is done relatively cold if inadvance lof theprecipitation step, or hot if concurrent with it, 'and 'may be'expedited by carrying out the carbonation under pressure. VIn the secondpart the ammonia evolved in the precipitation step is at least in partabsorbed in the barren liquor'fromthe precipitation step after cooling.

Having now described the effect of various lfac- 'tors on the novelsteps of our invention and indicated the basis for the improvementswhich We have made therein and which we wish to protect by letterspatent based on the disclosures of of the present application we willnow describe the practical application of the process.

A diagrammatic representation of one preie'rred form of the process'isshown in the gure.

In this flowsheet:

Step (l) represents the reduction of the higher manganese oxide contentof the ore to MnO, or

in the case of a carbonate ore,the conversion of the 'MnCOa content toMnO by heating. This step is effected `by heating to a suitabletemperature in a reducing atmosphere, such as hydrogen, natural gas,producer gas, or with Isuincient solid fuel or liquid hydrocarbons tomaintain such a reducing atmosphere. It may be performed in rotarykilns, multihearth furnaces, shaft furnaces, tunnel kilns or in avariety of other conventional or specially designed pieces (ui-heatingequipment.

Step (2) represents the cooling of the reduced ore to avoid there-oxidation that would-occur if the hot ore were exposed to theatmosphere. It maybe eiected by a device such as the Baker cooler, inwhich the reduced material, under a protective atmosphere, is advancedthrough a rotating, water-cooled cylinder, or by quenching in water, orby other conventional methods.

' Step (3) is the leaching step, in which the manganese is extractedthrough contact with solution 'made from NH3- andCOz containing someaccelerating 'agent such as ammonium sulphide. This step has been 'very`effectively carried on in closed tanks, agitated by a motor-drivenpropeller. It lends itself Well to a great variety of other conventionalequipment and methods, including percolation leaching, and in addition,be- 'cause'of the relatively 'short leaching period required, continuousleaching equipment such as rotating cylinders with internal baflles tolimit 'short-circui'tin'g may be used. This leaching step may be carriedon in cast iron or steel equipment without vthe equipment being attachedor the solution contaminated. This fact is one of the importantadvantages of the process as such equipment is inexpensive and 'readilyfabricated in any desired form.

Step (4) is a residue Vseparation step which yields clear pregnantliquor and tailings. Various types of iilters may be used in this step,though pressure filters 'are preferred because of the Apresence in thesolution o'f volatile ammonia. Excellent results lare also obtainablefrom thickeners, however, and any of the large number of conventionalpieces of equipment of this type may be used.l However, ltray-typethickeners are Considered particularly desirable for this step becausetheymay be completely closed off to prevent loss of the volatileammonia. Centrifuges of various -typesmay be used.

Step (5) is the carbonation of the pregnant liquor from step (4). Thisis effected by means of the cooled, oxygen-free kiln gases from thereduction step. It may be carried on in tanks using special absorptionequipment such as the Turbo-Absorber, in standard absorption towers, bydispersing the gases into a stream of fine bubbles by passing throughporous Alundum or fritted glass dispersers, or in other conventionalgasabsorption equipment. The carbonation step may also be carried outYunder considerable pressure.

Step (6) consists of the precipitation of MnCOa from the solution. Inone embodiment of the process, steps (5) and (6) are combined, thecarbonation of the pregnant liquor being carried out with kiln gas, thatis, hot enough to drive off the required amount of ammonia and to heatthe solution to a temperature of around 65 C. where completeprecipitation can be obtained. Under such conditions, the equipment usedwould be that described under step (5). Where the steps are carried onseparately, however, any conventional type of heat exchanger would besuitable. The equipment for the precipitation step may be made of ironor Steel but where a high purity of product is required'the steel ispreferably coated with a Y vitreous enamel. Stainless steel containingabout 20% C'r, 12% Ni and 2% Mo may be used 'without surface protectionand will not be attacked or contaminate the solution.

Step (7) is a separation of the precipitated MnCOa 'from the barrenliquor. Any type of vacuum or pressure lter would be suitable,preferably the latter because of the presence of volatile ammonia.Thickeners, however, are to be preferred since the MnCO3 settles veryrapidly, and the enclosed tray thickeners are very suitable.

vSteps (8) and (9) consist of the washing of the MnCO3 product to freeit of ammonia and ammonium carbonate. The first wash is an ammonia washto recover as much manganese as possible. The final washing is done withwater, this last being sent to the ammonia boiler for ammoniarecovery.These are standard chemical engineering steps involving standardequipment, such as tray-type counter-current decantation thickeners,washing filters, etc. All such equipment may be constructed of cast ironor steel.

Step (10) is the nal treatment of the product before shipment. Itrequires some control to minimize oxidation, and temperatures should bekept below 150 C. Where a particularly light-colored product is desired,vacuum dryers should be used; otherwise conventional drum, tube andshelf dryers are satisfactory.

Steps (l1) and (12) are the washing of the leach tailings for recoveryof the mother liquor. The iirst wash must be made with ammonia water,since addition of water to the tailing would precipitate the manganesein the mother liquor through dilution. The iinal washing is done withwater to recover the ammonia content of the liquor which had displacedthe mother liquor. The washing may be done by use of washing filters,but is preferably effected by thickening, the enclosed tray-typethickeners being particularly suitable. The managnese-bearing liquorfrom the ammonia washing step (11) may be alternatively added to thepregnant liquor in the carbonation step or sent to the ammonia absorberwith the barren liquor from step ('7) as shown in the figure. Which ofthese alternatives is adapted will depend on the amount of residue andthe ease with which it is washed. With a small amount of easily washedresidue the second alternative as in Example IV will be adopted;however, with a low grade ore and a consequently large amount of residuea counter-current washing method will be adopted and the liquorrelatively high in manganese content will be added to the pregnantliquor in the carbonation step. This is illustrated in EX- ample I.

Step (13) is an ammonia-recovery step in the process in which thevarious wash waters obtained from the treatment of tailings and productare collected and heated to recover ammonia. Almost any standard heatingor evaporating equipment is suitable for this purpose.

Step (14) is the cooling step designed for adjusting the temperature ofthe kiln gases to the desired value. Standard gas heating and coolingequipment would be satisfactory for such purposes.

Step (15) provides oxygen-free kiln gas to the system for make-up CO2.It consists simply of a bed of glowing coke through which the kiln gasesare passed to complete their reduction.

Steps (16) and (17) consist of ammonia and ammonia-CO2 absorptiontowers. These are standard, packed towers, as used throughout thechemical engineering industry.

Step (18) consists of condensation of the water from the gases evolvedin the precipitation operation.

Several examples will now be given of the application of the process tospecific ores.

EXAMPLE I For this example we take a manganese dioxide ore from theAppalachian region of the United States having the composition:

BaO

10 We reduce this ore in a stream of producer gas saturated with waterat 600 C. (1112 FJ. The reduction is carried out in an externally heatedalloy tube through which the reducing gas is passed.

The leaching of this ore is carried out in batches of 2000 pounds eachin steel tanks provided with motor driven agitators and gas tight coversconnected to an ammonia absorption system. For the leaching a solutioncontaining 3.5 mols of CO2 per liter and 16.0 mols of NH3 per liter isused. For each batch we use about 850 gallons of such solution. As anaccelerator we add 10 pounds of ammonium sulphide to each batch. About500 pounds of manganese is extracted to produce a solution containingabout '2'0 grams of managese per liter. The temperature rise is only 3C. above room temperature and the loss of ammonia is insignicant. Thetime to leach each batch is 20 minutes.y The slurry is thickened and 60%of the manganese removed in 510 gallons of clear solution. The thickenedresidue is washed with an aqueous solution of ammonia and CO2 containing12 mols per liter of NH3 and 3.5 mols of CO2 per liter in a series of ve1000 gallon tanks, the ammonia and CO2 solution pass'ingcountercurrentto the pulp. The manganese content of the solution as it leaves each ofthe i'ive thickeners is as follows:

Thickeners: g. /liter 1 50.0

The total solution recovered from the thickeners is accordingly 600gallons containing 34 grams per liter and 510-gallons containing '70grams per liter, that is, av total 1,110 gallons containing about 495pounds of manganese.

The residue is washed in a similar series of counter-current thickenersto recover the ammonia which is boiled oil` the wash water for reuse inthe system.

The solution is ready for the carbonation and precipitation step. Sincethis solution contains about 50 grams per liter of manganese, about 3.5mols per liter of CO2 and 14 mols per liter of NH3, it is carbonated bythe addition of 360 pounds of CO2 to provide for the CO2 to be removedas MnCOs in the precipitation step. It is then heated in a tank providedwith a stirrer and connected to the ammonia absorption system to 65 C.for three hours, whereby the ammonia concentration is reduced to 11.5mols per liter and about 1000 pounds of manganese carbonate precipitatedin a readily ltrable form. The manganese carbonate is filtered on awashing filter from the solution which then contains about 5.0 grams perliter of manganese, 11.5 mols per liter of NH3 and 3.5 mols per liter ofCO2. This solution is cooled and used for the absorption of the ammoniaand CO2 liberated at various points in the process.

The ltered manganese carbonate iswashed with a solution containing vl2mols of NH3 per liter and 3.5 mols oi- CO2 per liter to remove manganesedown to 0.10 gram per liter and the wash solution used along with thebarren solution from the precipitation step for the absorption ofammonia' and CO2. The carbonate is then washed with water which isboiled for the recovery of ammonia and CO2. Some of the ammonia and CO2evolved at various points in the 11 system is labsorb'ed in water ratherthan barren Yor Wash solution to provide the manganese free wash waterfor residue and carbonate. The Water balance in the system is providedby adjusting the amount discarded inthe wash waterv boiler vand theamount usedin the absorber for making the manganese-free washwater.

The manganese carbonate recovered in this way is a light pink 'color andis stable in air and when dried at 110'C., it analyzes as follows:

Percent Mn 44.2

CO2 35.2 H2O '7,2 Fe 08 Alkali metal-s .03

EXAMPLE II In`this'e`xainple we take 100`pounds of 'manganeseconcentrates from Chamberlain, South Dakota, analyzing:

Percent Mg 1.54 P205 l 1.56 Fe 12.72

S102 11.92 CO2 23.55

We heat this ore in aclosed rucible containing only a little charcoaljat800 C.'in order to drive off the COgand obtain the manganese in the formof` MnOtogether with oxides of iron, calcium and magnesium andthe other`constituents of the original ore. a

We, carry out'the solution step of our process on this ore by`addingthve'nely ground roasted ore to a`solution"containi ng 14.0 mols perliter of N Hg and '4.0 molsjper liter of CO2 to which CO2 isbeing'naddedso'as'tofmaintain the CO2 contentat all timesabove 3.5 molsper liter. The amount of CO2 which must be added is that which willcombine with the lime and'magnesia and iron present. rlhe 100 poundsofground ore is added to 30 gallons-of solution which contains one poundof ammonium sulphide, the solution and ore being agitatedduringtheperiod of addition. The resulting solution contains about 60 gramsper liter of manganese and represents anextraction of 87% ofthemanganese from the ore.

The solutionis 'allowed to stand several hours whereby any lime ormagnesiawhich is dissolved is precipitated.` 'The residue is thenseparated from the vsolutionj'by pressurelfiltration. The residueisfwa'shed With-:a 'solution containing 16 mols per liter ofiamu'ionlato remove' manganese and this wash solution'used together withthe barren solution from ythe'precipitation step for the preparation ofleaching solution for processing additional roasted ore. The residuerelatively free from manganese is heated to drive off am; monia and CO2which Yis 'absorbed `forre-use.

The pregnant solution containing about 12 pounds of manganese in 24gallons of solution is heated to C. for 20 minutes in a sealed iron tanklined with a plastic coating. Ninety-six percent of the manganese isprecipitated as carbonate. The carbonate is filtered and the barrensolution is used for making the next batch of lixiviant. The carbonateprecipitated in this way is so readily ltrable and the manganese isreduced to so low a value in the solution that the carbonate is vpressedas dry as possible on 'the filter and the washings discarded.

The carbonate obtained in this 'way analyzes:

Percent Mn 44.2 CO2 35.6 H2O '7.75 Fe .l0 CaO .20 MgO .08

The carbonate is'stable in air Aand may be dried at C. withoutdiscoloration.

En rMPLEII The cyclic nature of our process is illustrated by thefollowing example in which'an vAfrican ore having the following analysiswas used:

Percent Mn 48.92 Fe 4.10 Si 11.24 P- .18 CaO .26

This ore Vwas reduced prior to leaching by heating to 750 C. withanthracite coal. In this example the same lixiviant was used in 15cycles of operation, being regenerated after the precipitation step bythe addition of CO2 and NH3 to bring it to the original concentration ofthese constituents.

The procedure for-separating and washing the residue and for washing theprecipitate were the same as in ExampleI. INo attempt was made in thesetests, however, to recover and use NH3 and CO2 cyclically. lTheprecipitation step was carried on by heating in enamelled iron vesselsuntil the ammonia content had been reduced to l1 mols per liter. Theleaching step was carried on lin an ordinary steel tank. yIn each cycle2500 grams of reduced ore were used together with 19 liters of solutioncontaining 265 grams of NH3 per liter, gramsI of CO2 per liter, 1.8grams of manganese per liter and 11.0 gram of (NH4)2S per liter. Thebuild up of iron, alkali metals and second group metals, that is, thoseprecipitated by HzS in a slightly acid solution in the carbonate wasdetermined.

Extrac- Second Fc, por- Alkahs S, pcrv n T l 1 Cyde A0' 23st centpercent cont 93. 0 0.13 0.03 0. 01 Trace. .92.5 .l2 .03 .02 D0. r89. (i12 03 0l Dc. 90. 2 13 03 02 D0. 86.1 12 03 01 Do. 87.6 .13 .03 .03 D0.90.1 Y. 12 .o3 .01 Do. 91.2 .12 .03 .0l Do. 93.2 .l2 .03 .04 D0. A94.1.12 .03 .02 D0. 92.0 .l2 .03 '.01 D0. 91.8 .12 .03 .02 D0. 89.7 .12 .03.01 D0. 88.0 .12 .03 .0l vDo. 93.8 .12 .03 .02 D0.

13 It Will be seen that the impurities in the product remain constantindicating that the impurities taken into the leach step are held to aconstant concentration. This is an unusual and very desirablecharacteristic of a cyclic process.

EXAMPLE IV We take a relatively high grade ore having a coarse siliceousgangue and subject it to a reducing roast in a muiiied hearth furnaceusing oil as the reducing agent. The ore analyzed:

, Percent Mn 51.0 Fe 5.6 S102 12.2

One thousand po-unds of the reduced cre was extracted with 1000 gallonsof a solution containing 17.0 mols of NH3 per liter and 3.5 mols of CO2per liter. To the entire batch was added one pound of ammonium sulphide.Leaching was carried out in a steel tank with agitation and required 15minutes for each batch. The residue was sandy and easily settled,ltered, and washed. The total Weight of residue was 210 pounds. Theresidue was Separated on a washing lter and the recovered solution had avolume of 950 gallons and contained 95% of the manganese. The residuewas washed with four 50 gallon portions of ammonia solution containing12 mols per liter of NH3. The resulting residue contained less than 0.2%of the total manganese. The recovered solution was heated to precipitateMnCOs and drive off 40% of the ammonia and 25% of the Water. The gaseswere passed through a condenser and absorber to recover about 380gallons of ammonia solution containing about l2 mols per liter of NH3.

One thousand one hundred twenty pounds of hydrated MnCOa was separatedfrom the barren solution and the latter used to absorb ammonia and CO2evolved in other steps of the process and to absorb make-up CO2 and wasthereby regenerated for use in the leaching step of the process. TheMnCOs was washed with three 60 gallon batches of ammonia solutioncontaining 12 mols per liter of NH3. The soluble manganese in the MnCOawas thereby reduced to an insignicant amont. The ammonia wash solutionfor the residue and MnCOa wash were obtained from the condenser and thewash solutions from these operations mixed with the barren solution fromthe precipitation step to absorb ammonia liberated in other steps of theprocess. The residue and MnCOa after being washed with the ammoniasolution are washed with water and the wash water boiled to evolve NH3and CO2 which is collected in the ammonia absorber. No water is added tothe system by this operation.

The advantages of the process of our invention over our earlierdisclosures as well as over processes previously known in the art willbe obvious from the data and examples which we have given. In summary,however, it is pointed out that the process of the present inventionprovides the following advantages: f

(1) More rapid solution of the manganese oxide from the roasted ore.

(2) Higher concentration of manganese in the pregnant solution.

(3) More complete precipitation of manganese in the precipitation step.

(4) Manganese carbonate product pure and readily ltrable.

(5) Completely cyclic process without build up of impurities.

(6) Economy of heat since no solution need be heated above 65 C. and nowater is evaporated except as incidental to the precipitation operationand the boiling off of some ammonia and CO2.

('7) Since all solutions are ammoniacal, steel equipment can be used.

(8) The only chemical actually consumed in the process is CO2 which canbe supplied in the form of combustion gases, the heat of which is alsoutilized.

What is claimed is:

1. Process of recovering manganese as manganese carbonate from amaterial containing manganese in the form of MnO, which comprisesextracting the material with an aqueous solution containing at least 140g./l. of NH3 and at least 38.5 g./l. of CO2, in the presence of an addedagent selected from the group consisting of hydroxylamine salts, ferroussalts and soluble sulphides in an amount from 0.1% to 3.0% of the Weightof the manganese-containing material.

2. Process deiined in claim l, in which the reducing agent is ahydroxylamine salt.

3. Process defined in claim l, in which the reducing agent is a ferroussalt.

4. Process defined in claim 1, in which the reducing agent is a solublesulphide.

5. Process deiined in claim 1, in which the reducing agent is ammoniumsulphide (NH4)2S.

6. Process of recovering manganese as manganese carbonate from orecontaining manganese in the form of MnO which comprises extracting theore with an aqueous solution containing at least 140 g./l. of NH3 and atleast 38.5 g./1. of CO2, in the presence of an added agent selected fromthe group consisting of hydroxylamine salts, ferrous salts and solublesulphides in an amount from 0.1% to 3.0% of the weight of the ore, at atemperature between 10 and 30 C., separating the resultingmanganese-containing solution from undissolved residue, adding CO2 tothe solution in an amount at least approximately equal to the manganesepresent, reducing the ammonia concentration of the solution to less than12 mols per liter, heating the solution to at least 60 C. for at least30 minutes whereby to precipitate at least of the contained manganese asmanganous carbonate, separating the precipitated manganous carbonatefrom the solution, adding ammonia to the solution to raise its ammoniaconcentration to at least g./1., and reusing the solution in arepetition of the first step.

REGINALD S. DEAN. ABRAHAM L. FOX.

REFERENCES CITED The following references are of record in the le ofthis patent:

J. W. Mellors Modern Inorganic Chemistry, Single Vol. Ed., January 1935reprint of Eighth Edition, page 657, Longmans, Green & Co., N. Y.

1. PROCESS OF RECOVERING MANGANESE AS MANGANESE CARBONATE FROM A MATERIAL CONTAINING MANGANESE IN THE FORM OF MNO, WHICH COMPRISES EXTRACTING THE MATERIAL WITH AN AQUEOUS SOLUTION CONTAINING AT LEAST 140 G./1. OF NH3 AND AT LEAST 38.5 G./1. OF CO2, IN THE PRESENCE OF AN ADDED AGENT SELECTED FROM THE GROUP CONSISTING OF HYDROXYLAMINE SALTS, FERROUS SALTS AND SOLUBLE SULPHIDES IN AN AMOUNT FROM 0.1% TO 3.0% OF THE WEIGHT OF THE MANGANESE-CONTAINING MATERIAL. 